physics 2

Waves move energy from one place to another. In a progressive wave the wave front moves through the medium. There are two types of waves, transverse and longitudinal.

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Mechanical waves

occur in a medium (solid, liquid or gas).

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Transverse waves

are waves where the displacement of the particles in the medium is perpendicular to the direction the wave is travelling in.

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Longitudinal waves

are waves where the displacement of the particles in the the same direction as the wave is travelling in.

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Electromagnetic waves

are oscillating electric an magnetic fields they include radio waves, microwaves, infra-red, visible light, ultra-violet, x-rays and gamma rays. Electromagnetic waves are transverse waves and they all travel at the speed of light in a vacuum

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Transverse waves can be polarised but longitudinal waves cannot.

but longitudinal waves cannot. Unpolarised light is a mixture if waves in different planes. When this light is passed through a polaroid material only light waves in one plane are transmited and the light is now polarised.

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polarised examples

Polaroid sunglasses are popular with fishermen they reduce glare by blocking the reflected polarised light from the waters surface.

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wave properties

Amplitude (A) is the maximum displacement of a particle in a wave from its equilibrium position. It is measured in metres (m).

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wave properties

Frequency (f) is the number of complete waves passing a point in one second. It is measured in hertz (Hz).

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wave properties

Wavelength (?) is the distance between two identical points on a wave (i.e. one full wave). It is measured in metres (m).

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wave properties

Wave speed (c) is measured in metres per second (ms-1).

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wave equation

c=f(?) c = wave speed (m s-1) f = frequency (Hz) ? = wavelength (m)

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In Phase

Points on a wave which are always travelling in the same direction, rising a falling together, are in phase with each other.

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Out of Phase

Points on a wave which are always traveling in opposite directions to each other, one is rising while the other is falling, are in antiphase with each other.

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Path difference

If we measure the distance travelled by two waves and then compare those distances, any difference in the distances travelled is called the path difference. Path difference is measured in metres (m).

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Superposition of waves

When two waves pass through the same point they combine together to either constructively interfere with each other or destructively interfere with each other before passing on past each other and continuing their separate journeys.

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Constructive interference

The two waves are in phase with each other and constructively interfere to give a wave of greater amplitude.

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Destructive interference

The two waves are out of phase (anti-phase) with each other and destructively interfere to give a wave of zero amplitude.

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Stationary waves

Stationary waves are formed by two waves with the same frequency travelling in opposite directions.

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Interference

Laser light is a source of coherent monochromatic light.

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Coherence

two waves are coherent if the phase difference between them is constant. For this to be the case they must have the same frequency.

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Monochromatic

means having only one wavelength of light present.

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Young’s double slit experiment

When laser light passes through a slit it is diffracted. If there are two slits present the light will diffract at both slits. If a screen is placed on the other side of the slits from the laser an interference pattern is seen.bright and dark fringe

Diffraction happens when a wave hits an obstacle or gap, diffraction is greatest when the gap is about the same size as the wavelength of the wave. The waves bend round the object or spread out when they pass through the gap,called diffraction

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Single Slit Diffraction

When monochromatic laser light is shone through a narrow single slit a diffraction pattern is produced consisting of light and dark fringes. It produces a wide central bright fringe. The other bright fringe get dimmer as you move away from the centre

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Diffraction grating.

A diffraction grating is a piece of glass with lots of closely spaced parallel lines on it each of which allows light to pass through it, this is a transmission diffraction grating.